The compromise Freedom Tower unveiled in December 2003 was the result of a sometimes contentious collaboration between architects Daniel Libeskind and David Childs. Here is a look at some of the elements each brought to the design.

The Height and the Spire

Daniel Libeskind's early design for the Freedom Tower. (Reproduced with permission of the Lower Manhattan Development Corporation.)

The tower that Daniel Libeskind designed for his winning master plan was a 1,776-foot glass spire attached to a 70-story office building with a sloped roof. The spire would have contained hanging gardens, which is why Libeskind originally called this tower "Gardens of the World." After consultations with the Lower Manhattan Development Corporation (LMDC), the organization set up to facilitate the rebuilding of Lower Manhattan, Libeskind moved the spire so that it was placed asymmetrically on the west side of the building. But the height of 1,776 feet was a key point for Libeskind, who said, "The sky will become home again to a towering spire creating an icon that speaks to our vitality in the face of danger, and our optimism in the aftermath of tragedy."

As David Childs began designing his version of a skyscraper for Ground Zero in collaboration with structural engineer Guy Nordenson, the height fluctuated. As Childs told FRONTLINE in June 2004, he did not necessarily favor a building with the symbolic height of 1,776 feet. "The correlation between the number of feet in a building and of a date in history was quite abstract," he said, "… but that's important to the master plan that we mark that line."

By the end of November 2003, the design that Childs and Nordenson were proposing was a tower 1,776-feet tall with an antenna that would reach 2,000 feet. "I suggested this thing be 2,000 feet, because I knew that the higher it could be, the better it was in terms of broadcasting, and that the whole purpose of having something this tall was to create this platform for the antennas," Nordenson told FRONTLINE. But Libeskind thought a 2,000-foot tower would overwhelm his master plan, and insisted that the tower top off at 1,776 feet.

At the unveiling of the compromise design in December 2003 and again at the laying of the Freedom Tower's cornerstone in July 2004, LMDC officials insisted that the tower would end at the symbolic 1,776 feet -- a 1,500-foot building topped off by an asymmetrical 276-foot spire. But a July 2004 report in The New York Times suggested that matter may still be up in the air: while the building still will top off at 1,500 feet, the antenna may reach up to 2,000 feet. And Childs himself told FRONTLINE in a June 2004 interview that he was unhappy with the spire. "I wouldn't have an asymmetrical -- it's been called the toothpick or the bayonet. It's obviously a piece that is added to the corner," he said. "… This is the piece that has the least resolution, and we said that at the time of the unveiling in December and as we work our way up through the building, it still has the piece of least resolution. So I don't know exactly how that will be. I'm not happy with that, and wasn't, and I think there's some ways that that should get better. And that's true of all aspects of this building."

The "Twist"

Even before the competition to design the master plan was underway, Childs was already working on a design for a skyscraper at Ground Zero at the request of developer Larry Silverstein. Childs and Nordenson developed a design, which was incorporated into the compromise Freedom Tower, in which the tower tapers and twists around a concrete core, both providing stability to the building and allowing for unimpeded column-free interior spaces within. The exterior of the building is covered by a steel diagonal grid, which in addition to providing structural support against the wind, also sets in motion the tower's twisting form.

The compromise Freedom Tower, unveiled in December 2003. (Reproduced with permission of the Lower Manhattan Development Corporation.)

Childs says that the particulars of building in New York inspired the torqued shape of the Freedom Tower. "It gave a form that came out of the shape that was a direct result of the grid of New York and its peculiarities as it hit the slurry wall line," he told FRONTLINE.

The Windmills

Another feature of the torqued shape of the Freedom Tower is that it allows an opportunity to harness the winds from the Hudson River that sweep across the site. Working with engineer Guy Battle, Childs and Nordenson created a design in which a lacy system of steel cables, similar to the cabling on the Brooklyn Bridge, sits atop a 70-story office tower. The cabling houses a series of wind-harvesting turbines that will both provide an energy source for the tower itself -- an estimated 20 percent of the building's energy -- and minimize the wind's impact on pedestrians below.

The Statue of Liberty

In the introduction to his master plan, Libeskind wrote movingly of having caught his first glimpse of the Statue of Liberty when he arrived in New York as an immigrant. "I have never forgotten that sight or what she stands for," he wrote. "This is what the project is all about." Libeskind designed his original tower with an asymmetrical spire that would echo the Statue of Liberty's outstretched arm and torch. Throughout the back and forth of the design process with Childs, Libeskind insisted that the Freedom Tower would not conform to the master plan unless it retained the asymmetrical spire to reference the Statue of Liberty.

Childs and Nordenson, on the other hand, saw a stronger reference to the Statue of Liberty in the torqued tower they designed. "She steps forward. As you move your leg forward, your body twists," Childs told FRONTLINE. "And that's exactly what this form [of the Freedom Tower] does -- as it rises up, it twists."